The present invention relates to a thermal recording apparatus such as a thermal paper recording apparatus and a thermal transfer recording apparatus and, more particularly, to a thermal recording apparatus suitable for recording an image on large-sized recording paper.
As a conventional automatic drawing apparatus for drawing on large-sized paper of A0, A1 or the like, a pen plotter and a thermal recording apparatus with an in-line thermal head having an array structure are used. Because of a high-speed operation, low noise and easy maintenance, the thermal recording apparatus is frequently used. Since a long thermal head adaptable for A0- and A1-sized paper is low in manufacturing yield, its manufacturing cost is increased and its maintenance is difficult. Such a long thermal head cannot be easily put to practical use. For this reason, in the conventional thermal recording apparatus, a plurality of popular thermal heads such as heads for A3-sized paper are consecutively arranged in a line direction to record an image on paper having a large size such as A0 and A1.
In the conventional thermal recording apparatus, when an image is recorded on small-sized recording paper of A3 or the like, at least one of the plural thermal heads, which overhangs from the recording paper, is not supplied with a recording signal and thus it is not electrically driven. Nevertheless, the thermal head which is not electrically driven, is pressed against a platen roller, together with the other electrically-driven thermal heads, and it is mechanically driven.
Since the platen roller not only presses the recording paper against the thermal head but also feeds the paper by its rotation, its surface has a high frictional resistance. If the platen roller is pressed against the thermal heads without interposing any recording paper therebetween, the platen roller frictionally contacts the thermal head by its rotation and a resistance force is given from the thermal head to the rotation of the platen roller. As a result, a driving apparatus for rotating the platen roller has a drawback in which power required for rotating the platen roller is wasted.